It has recently been known (for example, L. D. Hicks et al., PRB 47 (1993) 12727 (NPL 1) and L. D. Hicks et al., PRB 47 (1993) 16631 (NPL 2)) or demonstrated (for example, L. D. Hicks et al., PRB 53 (1996) R10493 (NPL 3)) that Seebeck coefficient S and thermal conductivity K can be controlled by lowering a dimension of carriers (free electrons or free holes) and increasing phonon scattering owing to quantum wells and quantum wires.
A thermoelectric material in which carriers have further been lowered in dimension by forming particles has been known (Japanese Patent Laying-Open No. 2002-076452 (PTL 1)).
Furthermore, it has been reported as another example of a lower dimension of carriers (H. Takiguchi et al., JJAP 50 (2011) 041301 (NPL 4)) that by forming nanoparticles of SiGe in a thin film of silicon germanium gold (SiGeAu) by annealing the thin film, thermoelectric characteristics are improved as compared with bulk SiGe.